A fuel cell is an electrochemical energy conversion device that facilitates combining a fuel, such as hydrogen gas or a hydrocarbon, with an oxidizing agent, for example air or oxygen, in one or more chemical reactions to produce electricity.
A typical fuel cell includes an ion conducting membrane, such as a proton exchange membrane. The membrane separates a fuel on one side of the membrane from an oxidant on the other side of the membrane. The fuel is decomposed in a chemical reaction that liberates ions, typically protons, that travel through the membrane. After traveling through the membrane, the ions combine with the oxidant. The chemical reactions generate an electromotive force that can cause an electrical current to flow in an external circuit. A number of fuel cells are typically electrically connected in series to produce a desired output voltage.
A significant problem with many fuel cell designs is that they require many seals. Making reliable seals between the components of fuel cells in fuel cell stacks presents numerous technical problems. Some fuel cells have a large number of parts. Assembling such fuel cells can be time consuming and expensive.
Maintaining effective seals also presents problems in the design of other types of electrochemical reactor such as chlor-alkali cells or electrolysis cells.
Some fuel cell systems include frames which support a number of membrane electrode assemblies (“MEAs”) in parallel spaced apart relationship to one another. The frames include face seals which prevent fuel and oxidant from mixing with one another. FIGS. 1 and 2 schematically show prior art fuel cell systems 100 and 200. Fuel cell systems 100 and 200 include electrolyte membranes 104 supported by thin frames 102. Frames 102 are made of a suitable material, such as stainless steel.
Each membrane 104 is located between two frames 102. First and second face seals 110, 112 seal each frame to adjacent membranes 104. First and second electrically conductive catalyst layers 106, 108 are disposed on either side of each membrane. First and second gas diffusion media 114, 116 are also present.
Thin frame designs of the type illustrated in FIGS. 1 and 2 generally work well and have considerable design flexibility. Fuel cell systems 100 and 200 can provide multiple series-connected fuel cells in a structure that can be made thin. Such cells can offer satisfactory air-breathing fuel cell performance with diffusion being the major transport mechanism for both fuel and oxidant delivery.
Fuel cell systems 100 and 200 suffer from the disadvantage that they include numerous face seals 110 and 112, between frames 102 and the electrolyte membranes 104. The surrounding structure must provide adequate support to make face seals 110 and 112 reliable. Design features intended to provide support for face seals 110 and 112 typically occupy volume within a fuel cell system without increasing the power output of the system. Such features tend to make the fuel cell systems volumetrically less efficient than would be ideal. Decreasing layer thickness increases the number of cells per layer but increases the number of face seals 110, 112.
There exists a need for electrochemical reactors, such as fuel cells, chlor-alkali cells and electrolysis cells which are reliable and cost effective to manufacture.